Air and earth think differently: one lives on ideas and motion, the other on results and consistency. With respect, they complete each other — one's ideas land thanks to the other. Without it, one feels tied down and the other dizzy. Translation is the key.
One holds steady (fixed), the other flows (mutable): the fixed one gives the mutable roots, and the mutable teaches the fixed that changing isn't losing. Complementary — as long as neither caricatures the other as 'stubborn' or 'flaky'.